In recent years, with the progress in development of multimedia information, the transmission of not only audio data but also large-volume data such as still image data and moving image data has become common in cellular mobile communication systems. In LTE-Advanced (Long Term Evolution Advanced), in order to achieve large-volume data transmission, active studies have been carried out on techniques for achieving a high transmission rate using a broad radio band, a MIMO (Multiple-Input Multiple-Output) transmission technique and an interference control technique.
LTE-Advanced aims at high speed downlink communication using a maximum of 1 Gbps and thus requires a communication system that achieves a high throughput and is excellent in frequency utilization efficiency. LTE-Advanced promotes implementation of a high throughput cellular network and improvement of frequency utilization efficiency in the cellular network.
In order to improve frequency utilization efficiency, studies are being carried out on installation of a base station having a small cell radius called “picocell” (which may also be called “pico base station”) within a coverage area of a base station having a large cell radius called “macrocell” (which may also be called “macro base station”) (e.g., see FIG. 1A). However, although frequency utilization efficiency improves with the installation of the picocell, if the macrocell and the picocell have the same frequency band, the interference that the picocell receives from the macrocell becomes problematic. Studies are being carried out on setting an ABS (Almost Blank Subframe) which is a subframe that limits transmission of the macrocell to limit interference that the picocell receives. A subframe set as an ABS in the macrocell is called “protected subframe” and a subframe not set as an ABS in the macrocell is called “non-protected subframe in the picocell (see FIG. 1B). In the protected subframe, channel quality of the picocell improves.
Meanwhile, attention is being focused on network sharing in which a network is shared by a plurality of operators to reduce installation cost (e.g., see PTL 1 and NPL 1). With network sharing, equipment such as a base station (eNB) or the like or frequency band is shared among operators. Network sharing is expected to enable active and efficient use of finite resources such as the frequency band.